Greystone Property Development’s strategy resembles that of a truffle pig: It makes a living by searching where others don’t even bother to look.

This helps explain why the firm just became the first developer to bring new condos to City Island in more than 15 years.

In Manhattan and Brooklyn, Greystone has applied the same strategy of keeping its nose to the ground and sniffing out off-market deals with potential for profit.

The firm recently bought two sites in Clinton Hill where it will develop rental buildings. It is also turning a landmarked former public bathhouse in Gowanus into condos and building a rental tower on an adjacent parcel.

“Our strategy has always been to look for under-performing assets — for properties that are not in the market and opportunities that are not obvious to the street,” Simpson said.